Page 114 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:56 PM Page 90

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1.4.20 Well Design

rosion cracking. C75 can be used for H S service at all
2
temperatures, C95 at temperatures over 150˚F.
API P105/110 High strength steel. Suitable for H S service only above
2
175˚F.
API V150 High strength steel. Minimum yield stress 150,000 psi.
Not suitable for H S service.
2

1.4.20. Casing Connections

All connections serve to join lengths of casing together. However,
other characteristics may be important to your well.

1. Sealing mechanism. Is a premium connection required for the pro-
duction string? Buttress casing connections do not have a metal
to metal or elastomer seal; the seal is formed from the presence of
API HP modified thread compound in the thread roots. However,
the buttress thread form can be tin plated and then give an effec-
tive gastight seal rather cheaper than paying for premium
threads. There are Teflon-based thread compounds available (e.g.,
Liquid O Ring) which claim to form a gastight seal in a non-
premium thread.
Premium threads (VAM, NSCC, Hydril PH6, the various Atlas
Bradford, Fox, etc.) are mostly designed with a metal to metal
and/or elastomer seal that is energized in the last part of the tubing
makeup. Most operators require a premium thread for production
casing, liner, and completion tubing on gas wells.

2. Compatibility. Is it compatible with float equipment, hangers, etc.?

3. Strength. Does the connector impose limitations on tension or
burst? Refer to API Bulletin 5C2 or check the relevant casing design
table. Some connections are weaker than the pipe body in which
case the minimum connection yield strengths for burst and/or ten-
sion should be used in casing design calculations.

4. Availability. Can the thread be cut in locally or in the country? You

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